1. Field of the Invention
The present invention relates to a method for forming a thin film transistor (TFT) having a non-single crystalline semiconductor film. The thin film transistor according to the present invention may be formed on any of insulating substrates such as glass substrate or the like and semiconductor substrates such as non-single crystalline silicon substrate or the like.
2. Description of the Related Art
Recently, insulated gate type semiconductor devices having an active layer (referred to as an active region) of a thin film on an insulating substrate have been studied. In particular, insulated gate transistors of a thin film, or so called thin film transistors (TFTs), have been studied assiduously. These are grouped into amorphous silicon TFTs and crystalline silicon TFTs, depending on the semiconductor materials to be used and the crystal conditions of the materials.
Crystalline semiconductors have a larger field mobility than amorphous semiconductors and therefore may be adapted to high speed operation. Using a crystalline silicon, since not only NMOS TFTs but also PMOS TFTs are formed, CMOS circuits can be obtained. For these reasons, TFTs using crystalline silicons have been studied generally in these days.
From the technical results up to this time, an insulated gate film of a silicon oxide to be formed by thermal oxidation has the most preferred characteristics in a case wherein such insulated gate type devices (elements) are fabricated. However, in order to obtain the thermal oxide film, heat treatment at temperatures of around 1000.degree. C. is needed. Such temperatures limit the substrate materials to be used. Therefore, for forming such TFTs, insulating films to be formed by sputtering or various chemical vapor deposition (CVD) methods are used.
Since the formation of these insulating films does not need such high temperatures, it solved the limitation of the usable substrates. On the other hand, however, the insulating films to be formed by such chemical vapor deposition methods are found to involve other problems that they have a high interfacial level density and have many defects such as pin holes, etc. In repairing the defects and improving the characteristics of the films, the film cannot be treated after the film forming and the optimal film forming conditions are the only one manner to solve the problems at present. The present invention has been made in consideration of the current situations in this technical field, and it provides a method for forming TFTs having improved characteristics by repairing the insulating film after its film forming and improving the characteristics of the interface between the insulating film and a semiconductor or between the insulating film and a gate electrode material.